1. Filed of the Invention
The invention concerns a directional control valve including snap-locking means for retaining the slide of a directional control valve in at least one switching position in accordance with the preamble of claim 1, and snap-locking means tor a like directional control valve.
2. Discussion of the Background
This type of valve means is utilized for example in agricultural vehicles having hydraulic auxiliary attachments. By the generic valve arrangements, a three way use is to be achieved, namely to enable conventional control of the lifting cylinder of auxiliary equipment, such as e.g. of a front loader, via the valve arrangement. Another desired use is to control other auxiliary equipment, such as e.g. a hydraulic motor via the valve arrangement, wherein the hydraulic fluid supply is controlled through the directional control valve which is to be lockable in two end positions through snap-locking means in accordance with the rotating direction of the hydraulic motor. The third use, finally, is that in particular applications the snap-locking function is to be cancelled, e.g. by being pushed out when the end position of a hydraulic cylinder is reached. This "pushing out" is commonly referred to as "kick-out". I.e., the generic valve arrangement is to enable constant latching of a valve slide of the directional control valve, cancellation of the latching engagement when a predetermined load pressure is exceeded, and a mode wherein the effect of the snap-locking means is cancelled entirely.
EP 0 394 860 B1 discloses a valve arrangement including a directional control valve and snap-locking means whereby the above mentioned triple use is provided for. To this end, there is provided in the directional control valve slide an axial bore wherein a snap-locking piston of an engagement part is received, whereby latch members may be biased in corresponding grooves of the valve housing through the peripheral wall of the directional control valve slide. Control of the snap-locking piston is carried out by means of a valve slide of a kick-out arrangement, whereby a system pressure may be supplied to the snap-locking piston in order to establish the locking engagement. When a predetermined system pressure is exceeded, a connection to a tank is opened through the slide of the kick-out arrangement, so that the pressure supplied to the snap-locking piston is relieved and the locking engagement is cancelled. The triggering force of the kick-out arrangement can be adjusted by an operator through setting means. For example, constant latching, kick-out upon exceeding a predetermined control pressure, and cancellation of engagement by adjusting a minimum triggering force may be preselected in the known valve arrangement through a corresponding adjustment of the triggering force.
Such a variation does, however, have the drawback that the slide must be provided with an axial bore for receiving the snap-locking piston, and with corresponding connection lines to the kick-out arrangement accommodated in the valve housing, whereby considerable expenses are incurred in production owing to the small dimensions of the directional control valve slide. The same is true for the components establishing the locking engagement as these have to extend through the peripheral wall of the directional control valve slide. It must be regarded another drawback of the conventional system that the operating condition in which the effect of the snap-locking means is cancelled is only possible when a corresponding triggering force ensuring immediate triggering of the kick-out arrangement is set at the kick-ut arrangement by way of the setting means. This means that in order to adjust this condition, the operator must in a most unfavorable case pass through the entire adjustment range of the setting means, i.e. the range from maximum triggering force to minimum triggering force.
Neither can the other known directional control valves comprising snap-locking means overcome the above described drawbacks.
Thus from GB-A-1227539 a valve arrangement is known wherein adjustment is only possible between constant locking engagement of the snap-locking means and a position wherein the locking engagement is cancelled. That is, a kick-out function is not provided in this known valve arrangement.
From U.S. Pat. No. 3,132,668 a valve arrangement is known wherein a kick-out function is provided, however switching between an engagement position and a position wherein the locking engagement is cancelled cannot be carried out by the operator.